Since the introduction of Bitcoin---the first wide-spread application driven by blockchains---
the interest of the public and private sector in blockchains has skyrocketed. At the core of this
interest are the ways in which blockchains can be used to improve data management, eg, by
enabling federated data management via decentralization, resilience against failure and
malicious actors via replication and consensus, and strong data provenance via a secured
immutable ledger. In practice, high-performance blockchains for data management are …

The problem of sending a value v from a cluster C1 to a cluster C2 such that▶ all non-faulty
replicas in C2 the value v;▶ all non-faulty replicas in C1 that the value v was received;
and▶ C2 only receives a value v if all non-faulty replicas in C1 upon sending v.